This invention relates to amplifiers and more particularly to high gain differential amplifiers and to their use in comparators. Differential amplifiers are known in the prior art which provide amplification of D.C. or low frequency signals over a wide temperature range. This wide range of operating temperature is achieved by making the amplifier symmetrical. Due to the symmetry, various temperature dependent error signals tend to cancel. Examples of these temperature dependent parameters include a transistor's current gain .beta., saturation current I.sub.co, and base to emitter voltage V.sub.be.
A variety of differential amplifiers exist in the prior art. One widely used circuit is called the Darlington amplifier. These and other differential amplifiers all have the desirable feature of being relatively insensitive to temperature changes. However, a disadvantage of the Darlington circuit and other known differential amplifiers is that they do not use positive feedback to improve their voltage gain. As a result, a single stage of amplification may give less gain than is desired. In comparison, by the teachings of this disclosure, the gain of a single stage Darlington differential amplifier can be increased by a factor of 10.
Accordingly, it is one object of the invention to provide an improved differential amplifier.
Another object of the invention is to provide a differential amplifier using positive feedback to increase its gain.
Another object of the invention is to provide a differential amplifier comprised of a pair of transistors for sensing any difference in voltage across their base to emitter junctions and for supplying collector currents to increase the voltage difference.
Still another object of the invention is to provide an improved comparator that includes a differential amplifier having positive feedback to increase its gain.